Metal push belt and oil specification related thereto

ABSTRACT

A composite driving belt provided with a carrier and a plurality of transverse elements assembled slidably thereon, the carrier including one or more bands, preferably composed of a plurality of endless metal bands disposed radially around each other, each element being provided with a radially outward directed carrier contact plane for contacting a radial inner contact plane of the carrier while in operation, wherein the contact plane of both the carrier and the element have a non profiled surface. In particular the roughness and shape of the relevant contacting faces of a belt are adapted to achieve a hydrodynamic lubricating condition, while the lubricating oil is defined to meet the requirements of an improved efficiency push belt.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division of application Ser. No. 10/028,427, filedon Dec. 28, 2001 now U.S. Pat. No. 6,695,732, the entire contents ofwhich are hereby incorporated by reference

BACKGROUND OF THE INVENTION

The invention relates to a composite driving belt provided with acarrier and a plurality of transverse elements assembled slidablythereon.

DESCRIPTION OF THE RELATED ART

Such Belt is generally known, e.g. described in U.S. Pat. Nos. 3,720,113and 4,080,841. In the known belt, a carrier, alternatively denotedtensile element or tensile means, is composed as a package of a numberof endless metal bands. The known belt may in particular be applied in avariable transmission, whereby the driving belt runs over pulleys, thesubstantial conical sheaves of which are adapted to be displaced axiallyrelative to each other so that the running diameter of the driving beltover the pulley may vary. In turn, while the belt is in operation, thecarrier or band package slides over a contact face, the so-called saddlepart of the transverse elements. Also, the separate bands of the packageslide relatively to each other during operation.

In practice the driving belt, in particular each of the bands, is undera very high tension, on the one hand to ensure a proper frictionalcontact between the pulleys and the transverse elements and on the otherhand to properly conduct the transverse elements in the straight part ofthe driving belt, i.e. to prevent the belt, in particular the transverseelements in the straight trajectory part of the belt from splashingapart.

The efficiency of such Belt is rather high, but internal losses in thedriving belt remain as result of frictional forces between the variousparts, and as a result of such friction dissipated heat is to beremoved. To meet these phenomena, the belt is in practice required torun in an oiled environment.

One manner of addressing these practical problems is addressed byEuropean patent application 0014014, which shows a manner of drainingoil to the locations where sliding contact may take place and where heatis to be removed. The main important contact areas dissipating heat arebetween pulley and transverse element, between saddle and tensileelement and between the bands of the tensile element. According to theteaching of this publication, one flat side of each band should beprofiled, such that when incorporated in a belt, this side abuts a bandside without such profiling. In this manner an important oil drain isachieved by the profiling towards both sliding contacts in which a bandis involved, viz. Mutually between the bands, and between the inner bandof a carrier and the saddle of transverse elements.

The document thereby teaches that an improved mutual friction betweenthe mutual bands disposed around each other leads to an efficiencyincrease.

From commercialised belts it is found that such profiling is applied onthe inner side of such constituent metal rings of a band. This practiceis also suggested by the figure of said EP publication and is confirmedby the recent patent publication EP-A-0909907.

A draw back of the known belts is that when the belt is operated inrotation transfer modes outside medium, i.e. outside ratio 1, theefficiency decreases, in particular when the belt is operated close toso called low (LOW) or over drive (OD) mode. It is an object of thecurrent invention to address this phenomenon, i.e. to improve theefficiency in these areas in a safe and reliable manner, i.e. withoutendangering the proper oiling of the various sliding contacts related tothe functioning of the known belt.

SUMMARY OF THE INVENTION

According to the invention this may in particular be reached by aconstruction in accordance with the features disclosed herein. Aconstruction having the feature of the invention surprisingly directsaway from above said common practice of contacting, realises an improvedoverall efficiency through a decreased amount of friction in the abovesaid ranges, already by the mere omission of the oiling profile.Moreover, the measure according to the invention enhances the belt'slifetime by virtue of the effect that the decreased amount friction alsooccurs in the much-used parts of a transmissions range of ratios. Thusaccording to an insight partly underlying the invention, a distinctionshould be made between the shape of contact faces required in aband-band contact and in a band-element contact. The radial inwarddirected carrier surface is relatively very smooth, at least diminishedby a half compared to the roughness from known belts, while apredetermined profiling is omitted from this surface, i.e. no separateaimed treatment of the profiling can be recognised in the surface.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be explained further by way of example along adrawing in which:

FIG. 1 represents a single ring of prior art belt;

FIG. 2, in a view according to FIG. 1 represents a belt in accordancewith the invention;

FIG. 3 is a tribological graph realised by research underlying theinvention, and providing the insight upon which the invention is based;

FIG. 4 represents a radial cross section of a belt, showing a transverseelement and the tensile means cross section

FIG. 5 is a cross section of the transverse element along the line V—Vin FIG. 4, while

FIG. 6 more in detail provides the cross section of the so-called saddlepart in FIG. 5, alternatively denoted tensile means contacting face, inaccordance with the invention.

FIG. 7, is a graph illustrating the efficiency characteristic of a beltin various drive ratios.

In the figures corresponding components are denoted by identicalreferences.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 and 2 represent rings of a drive belt, in particular push beltas commonly known. The rings are in common applications like automotivepersonal vehicle and trucks, utilised in a nested arrangement of aplurality of circumscribing loops or rings, as may e.g. be taken fromFIG. 4. Such a set of nested rings forms part or all of the belt'stensile means along which transverse elements are disposed freelymoveable in the endless longitudinal direction of the belt. The elementsare clamped between the sheaves of a set of pulleys and transmitrotation from one drive pulley to a driven pulley. The tensile meansthereby serves to keep together the transverse elements pushing againsteach other.

When the driving belt runs over pulleys having different runningdiameters, the variable bands of the band package have a mutual speeddifference, at least in situ of one of the pulleys. This speeddifference may in practice be more than 1 meter per second between twosuccessive bands disposed a round each other. Moreover, notably theinner bands of a carrier are pressed on to each other with substantialforce, since the pressure force on a band is built up by all bandsdisposed outside i.e. there around.

By providing in particular the more inwardly disposed bands at least atone side with a surface profiling, through which an improved lubricationbetween the bands will be produced, an efficiency improvement occurs.Preferably, the surface profiling comprises grooves, which in practiceprovide good results. According to a further feature, the rougheningvalue of the surface profiling lies between 0.30 and 0.75 μm Ra, heremeasured according to CLA method, and preferably between 0.46 end 0.55μm Ra.

In a preferred embodiment provided in FIG. 2, the grooves are, like inthe known belt, disposed in crossing sets, however at the radial outerside of the belt. A good result is achieved when the variable bands areprovided with the surface profiling only at the outer one flat bandside, while the radial inner side is provided relatively very smooth.The grooved profiling of the outer side of a metal band is achieved byrolling a band between rollers, one roller being fitted with a surfaceprofiling on the circumferential surface.

The drawing in FIG. 1 diagrammatically shows an endless metal band. Thewidth of such a hand may e.g. range between 5 and 20 mm and thethickness between 0.15 end 0.25 mm. The diameter of the band in circularcondition may e.g. range between 150 and 400 mm. The endless band has anexterior side 2 and an interior side 1. In the known embodiment of FIG.1, the interior side 1 is provided with a surface profiling of crosswise disposed grooves, whereas in the embodiment according to theinvention this profiling is made to the exterior side 2 of a ring of abelt. In this manner, a band-element contact is made by the flat side ofthe ring. According to a preferred embodiment of the invention all ringsof a belt's tensile means are incorporated in this manner.

It is further derived from the investigations underlying the currentinvention that contrary to the known manner of lubricating the contactbetween a carrier face and the saddles of the transverse elements abetter performance is achieved alternatively at applying a combined setof measures. According to this set of measures, for lubrication of thiscontact should be relied on a natural flow of oil between element andcarrier in combination with a very much smoothened surface area of bothcontacting faces, i.e. saddle face and the inner band facing of acarrier. However according to the invention, primarily, the smoothening,expressed in roughness index Ra, of both faces should be such that theso-called combined roughness Ra′, i.e.Ra′=SQRT(Ras ² +Rar ²)  (1)where

-   -   Ra′=the reduced roughness index    -   Ras=the average roughness index of the saddle surface expressed        in Ra.    -   Rar=the index for the average roughness of the inner ring face        contacting the saddle.    -   SQRT=square root of ( . . . )        meets the requirement to remain smaller than 0.5 μm, preferably        to remain within the area smaller than 0.25 μm.

FIG. 3 diagrammatically reflects a curved typical relation according tothe invention between a friction coefficient or index, linearly indexedalong the Y-axis of the figure, and a “belt and oil features” index L,alternatively Lubrication number L, logarithmically indexed along theX-axis. The index L is calculated utilising the formula:

$\begin{matrix}{L = \frac{\eta_{0}V_{r}}{p_{av}R_{a}}} & (2)\end{matrix}$in which:

-   -   L=a lubrication number or index in accordance with an insight        underlying the invention;    -   Vr=the relative speed between the two contacting surfaces, here        of the inner belt ring and a transverse element's saddle;    -   η₀=the dynamic viscosity index of the lubricating medium;    -   Pav=the average Hertzian stress within the band/saddle contact;    -   Ra=the combined surface roughness Ra′ of both saddle and ring        surface.

The combined surface roughness' is alternatively denoted reducedroughness is calculated in the ordinary manner in the art providedabove, expressed in roughness coefficient Ra′.

The principal characteristic of the curved relation given by formula 1and FIG. 3 is according to the invention determined by dominantparameters Vr, and Ra, whereas the viscosity and the average Hertzianpressure parameters are in accordance with the insight according to theinvention not, at least not directly related to design parameters of thebelt. The formula (2) according to the invention more in particularreveals that relative speed Vr is the most dominant factor forinfluencing the friction coefficient since also Ra is given once thebelt is set into operation.

FIG. 3 shows in accordance with experimental results of researchunderlying the invention and matching the index line of formula 1, thatthe relation between an actual friction coefficient and the lubricationindex appears to typically follow a curve with three main sections. Inthe first section BL, suggestedly where so called boundary lubrication,i.e. shearing contact exists between the two contacting surfaces, thefriction coefficient is virtually constant with increasing index L. In asecond section ML, suggestedly where mixed lubrication and frictionoccurs, the friction coefficient drops with increasing L number,typically from somewhere like 0.18 to somewhere like 0.01. In the thirdsection HL, where suggestedly hydrodynamic lubrication exists, i.e. withshear occurring within the lubricant and not between the contactingsurfaces, the actual friction index has it's lowest value and again isvirtually constant or may slightly increase again with increasing valueof L.

FIG. 7 diagrammatically shows the efficiency curve of a known belt. Itreveals that efficiency is lowest towards the extreme ends of a typicalratio range, i.e. between overdrive ratio area OD to the left of thegraph and low drive ratios area LOW to the right of the graph. In theexemplary graph typical values for ratio i at LOW are around i=2.4 whileat OD area ratio i is around i=0.5. Highest efficiency occurs in Mediumratio with i=1. With the measure in accordance with the invention, i.e.with fully smooth contacting faces of preferably low roughnesscontacting each other, the efficiency of the belt is increased by anamount within the higher part within the range between 0.25 and 1% ofefficiency increase, whereas the extreme ends of the ratio range show anincrease of values within the lower part of the range. The overallincrease in efficiency is of considerable significance at long lifeoperation of the belt.

The efficiency increase achieved by the primary, above-mentioned measureis in accordance with a further, separate though here combined measureaccording to the invention achieved by a specific shaping of thetransverse elements saddle. This measure in particular, i.e. mostlyeffects the belt efficiency towards the LOW and OD sides of the ratiorange. The measure is illustrated by the drawing in FIG. 7, described inthe following.

FIG. 4 provides a cross section of a belt and a view of a transverseelement known per se, depicted according to a view in the longitudinaldirection of the belt. FIG. 5 is a transverse cross section thereof overthe line V—V, with the tensile means being omitted from the drawing,providing a view in a belt's axial direction. FIG. 6 in an enlargedscale depicts the in FIG. 5 encircled part of the element, in fact thepart which contacts the inner face of a belts tensile means, the socalled saddle of an element, here shaped in accordance with theinvention. In FIG. 6 the tensile means is shown.

In the saddle according to the invention the contacting face is shapedso as to realise both a line shaped contact between tensile means andsaddle and a wedge shaped space (WS) between the relevant contactingelement and the portion of the tensile means extending over the relevantelement. According to the invention, in this manner lubricating medium,at normal operation applied constantly to the belt, may be collected ina manner so as to have a concentration at a point, i.e. an axial line ofcontact between the tensile means and the saddle. With thisconcentration of lubricating medium, sufficient amount of medium isensured for realising the conditions to achieve a so-called HydrodynamicLubrication in the contact between saddle and tensile means. The saddleis also shaped such so as to achieve the same condition also in caseswhere the relative movement between saddle and tensile means in thelongitudinal direction, depending on the operating conditions of thebelt, may temporarily be reversed. At achieving the said lubricatedcondition in the said mutual contact, use is made of the insight thatthe element and the tensile means each have a different effective radiusof rotation within a pulley, so that relative difference Vr in velocityof each belt component occurs, thereby creating the possibility ofhaving a lubricated contact. To achieve such condition, the saddle is inaccordance with the invention, as taken in cross section, provided withan elliptical shape. In this manner, with respect to a lubricatedcontact, even at the circular trajectory with smallest radius of a beltwithin a transmission, a sufficient amount of wedge shaped spacing, theso called entry space, between the tensile means and the saddle isguaranteed before the mutual contact takes place.

It will be evident from the preceding description that it is a furtherprerequisite in accordance with the invention that for achieving thedesired condition in the mutual contact, the local bending radius Rb ofthe band, i.e. tensile means, and of the saddle Rs may not be equal,thus:Rb< >Rs  (4a)while alsoRs<Rb  (4b)

In accordance with a further aspect underlying the invention, thecombined local radius, i.e. the reduced radius of both the saddle andthe tensile means is taken into consideration by the requirement:1/Rr=1/Rs+1/Rb  (5)Where

-   -   Rr=the reduced radius of a Carrier and Saddle face contact    -   Rs=the local radius of the saddle measured in mm    -   Rb=the instantaneous radius of the band measured in mm

It is in accordance with the invention considered that for mostapplications of a belt, generally Rs should range up to 25 mm, whereasRr for commonly applied transmissions typically ranges between 25 and 80mm during operation of the Belt. Both the radii are taken in accordancewith the radial and longitudinal direction of a belt, considering thenormal operation and configuration thereof in a pulley. More inparticular it is considered that for realising the said wedge shapedentry space at the largest amount of possible contacting locations on asaddle, as taken in longitudinal direction of the belt over the saddlesurface, without the radii of saddle and band becoming equal, the saddleshould according to the preferred embodiment be shaped elliptical, withthe ellipse extending over virtually the entire thickness of an element,thereby obviating non-continuous transitions in a possible contactingsurface since from experience underlying the invention it is known thatthese will break, i.e. remove the lubricated condition in the mutualcontact. Thus, in dependence of an elements thickness, the saddle isshaped so as to at least largely, e.g. within 90% reliability,correspond to the shape of a half ellipse, the corresponding ellipsebeing defined by the mathematical formula for an ellipse and departingfrom the prerequisites in accordance with the insights underlying theinvention according to which, the ellipse largest width corresponds tothe elements width, while the derived local radius of curvature at theellipse largest height should be smaller than the smallest possibleradius of curvature of the belt. In this manner, also a continuoustransition from the elements principal face to the saddle is achieved,i.e. by an infinitely small radius of curvature.

The invention particularly aims at realising a generally applicabledesign rule. Thus it is taken that for most applications a minimumelement thickness will be 1.5 mm, while a smallest radius of curvature,either defined by the physical features of the belt or by the smallestdiameter of transmission shafts over which the belt will run, will beabout 25 mm. It is to be understood that in the latter respect thespecification of the belt, i.e. the prescribed boundaries of use takeprecedence over the radius that a belt may actually presume due to it'sphysical characteristics. Thus in accordance with a preferred embodimentand design rule of the invention, a generally applicable shape isattained of which the largest diameter through the elliptical centre is1.5 mm, the shortest diameter about 0.046 mm or smaller, while the localradius of curvature concurring with the line of the said shortestdiameter is 25 mm or smaller, while the radius of curvature over theline concurring with the line of the said largest diameter, is 6.75 E-4mm, i.e. infinitely small, thus obviating a non-continuous transitionfrom an element principle plane to the saddle surface.

For even better performance of a belt and transmission in accordancewith the invention the invention provides to apply an lubricating mediumin the form of an oil type having a dynamic viscosity η larger or equalto 9 MPa*s at a nominal temperature of 100 degrees Celsius, preferablyalso having a kinematic viscosity ν larger than or equal to 10 E-6 m²/s.In this manner all factors influencing the quality and efficiency ofoperation of a belt are optimised, more importantly, are brought into afunctionally safe area.

In the latter respect, according to a further aspect of the invention,the so-called rocking edge of the belt is provided below 1 mm from thesaddle surface, more in particular in a range between 1.25 and 2 mmbelow the saddle surface. In this manner it is achieved to increase therelative velocity Vr between saddle and tensile means, alternativelydenoted carrier, in particular at the extreme OD and LOW ends of therange of ratios in which the belt will operate. In combination with any,preferably all of the previous measures this measure appears to increasethe belts efficiency, in particular in these LOW and OD areas in whichthe belt may operate most of its operating time.

The invention further relates to all details of the figures pertainingto the description and all features defined in the following claims.

1. A composite driving belt provided with a carrier and a plurality oftransverse elements assembled slidably thereon, the carrier comprisingone or more bands disposed radially around each other, each elementbeing provided with a radially outward directed carrier contact planefor contacting a radial inner contact plane of said carrier while inoperation, wherein, the carrier contact plane of the element, as seen inside elevation, is provided over a major part of a width of the elementand is provided with a convex curvature for contacting the carrier innercontact plane, the convex curvature defined by at least substantiallycorresponding to the shape of a non-circular half ellipse, thecorresponding ellipse being defined by the mathematical formula for anellipse in which the ellipse's largest width corresponds to the width ofthe element and the local radius of curvature at the ellipse's largestheight is smaller than the smallest radius of the curvature of the belt,the belt is constructed for operation in a lubricated environment with alubricating medium collected between the carrier contact plane and thecarrier during operation in all drive ratios of the belt, wherein, i)the carrier contact face of an element is shaped such that the contactbetween an element and the carrier, under all operating conditions ineach drive ratio of the belt, defines a wedge shaped space between thecarrier contact face of the element and the contact face of the carrier,and ii) said elliptical shape of the carrier contact plane defines thewedge shape to collect a lubricating medium between the carrier contactplane of the element and the carrier during operation in all driveratios of the belt to provide a concentration of lubricant at an axialline of contact between the carrier and the element in which shearingoccurs within the lubricant and no shearing occurs between anycontacting surfaces of the element and carrier.
 2. Belt according toclaim 1, characterised in that the combined roughness Ra′ of both thecontact plane of the element is lower than 0.10 μm.
 3. Belt according toclaim 1, characterised in that the roughness of the inner contactingface of the carrier is of a value lower than 0.2 μm.
 4. Belt accordingto claim 1, characterised in that the roughness of the inner contactingface of the carrier is of a value lower than 0.10 μm.
 5. Belt accordingto claim 1, characterised in that the contacting face of the carrier, atleast once having run for two hours in a most accelerating transmissionratio (OD) within a transmission for which the belt is designed, has aroughness equal to or lower than 0.05 μm.
 6. Belt according to claim 4,characterised in that each contacting face, of the carrier and theelement, has a roughness equal to or lower than 0.05 μm.
 7. Beltaccording to claim 1, characterised in that the radius of curvature atthe elements cross centre is smaller than the smallest radius ofcurvature allowed for the belt.
 8. Belt according to claim 1,characterised in that the curvature extends entirely over said elementcontact face as seen in side elevation.
 9. Belt according to claim 1,characterised in that the maximum height of the saddle is smaller than0.025 mm.
 10. Belt according to claim 1, wherein the bands have apredetermined surface profiling, and the roughness value of the surfaceprofiling ranges between 0.30 and 0.75 μm Ra.
 11. Belt according toclaim 10, characterised in that the surface profiling is realised bygrooves disposed in crossing sets.
 12. Belt according to claim 1,characterised in that a rocking edge of each transverse element is setmore than 1 mm below the saddle surface.
 13. Belt according to claim 11,characterised in that a rocking edge is located in a range between 1.25and 2 mm below the saddle surface.
 14. Transmission provided with a beltaccording to claim 1, wherein the lubricated conditions provided by alubricating oil are characterised in that the lubricating oil has adynamic viscosity η larger or equal to 7 MPa*s, at a nominal temperatureof 100 degrees Celsius.
 15. Transmission provided with a belt accordingto claim 1, wherein the lubricated conditions provided by a lubricatingoil, characterised in that the lubricating oil has a dynamic viscosity ηlarger or equal to 8 MPa*s, at a nominal temperature of 100 degreesCelsius.
 16. The belt of claim 1, wherein the contact plane of both thecarrier and the element have a relatively smooth surface.
 17. Acomposite driving belt, comprising: a carrier comprising plural bandsdisposed radially around each other; and a plurality of transverseelements assembled slidably on the carrier, each element being providedwith a radially outward directed carrier contact plane for contacting,while in operation, a radial inner contact face of said carrier, eachelement having an element width, wherein, said radially outward directedcarrier contact plane, as seen in side elevation, extends over a majorpart of the element width, said radially outward directed carriercontact plane has a convex curvature for contacting said carrier innercontact face, the convex curvature at least substantially correspondingto a shape of a non-circular half ellipse, the correspondingnon-circular ellipse being defined by a mathematical formula for anellipse in which the ellipse's largest width corresponds to the elementwidth and a local radius of curvature at the ellipse's largest height issmaller than a smallest radius of the curvature of the belt, wherein,the belt is constructed for operation in a lubricated environment with alubricating medium collected between the carrier contact plane and thecarrier during operation in all the drive ratios of the belt, and thenon-circular ellipse being shaped to collect the lubricating medium tocreate an elasto-hyrodynamic lubrication condition between the carriercontact plane and the carrier in all the drive ratios and to develop alayer of lubrication fluid between the carrier contact plane and thecarrier with shearing occuring within the collected lubricant betweenthe carrier contact plane and the carrier and no shearing occurringbetween contacting surfaces of the carrier contact plane and thecarrier.
 18. A composite driving belt, comprising: a carrier with a bandhaving a radial inner contact face; and plural transverse elementsslidably mounted on said carrier, each element having a radially outwarddirected carrier contact face for contacting said carrier radial innercontact face, each element having an element width, said radiallyoutward directed carrier contact face, as seen in side elevation,extending over a major part of said element width, said radially outwarddirected carrier contact face having a convex curvature for contactingsaid carrier inner contact face, the convex curvature corresponding to ashape of a non-circular half ellipse, wherein, the belt is constructedfor operation in a lubricated environment with a lubricating mediumcollected between the carrier contact plane and the carrier duringoperation in all drive ratios of the belt, the carrier contact face ofan element is shaped such that contact between each element and thecarrier, under all operating conditions in any drive ratio of the belt,defines a wedge shaped space between the carrier contact face of eachelement and the contact face of the carrier, the wedge shape collectsthe lubricating medium between the carrier contact plane of the elementand the carrier during operation in each drive ratio of the belt to havea concentration of collected lubricant at an axial line of contactbetween the carrier and the element in which shearing within a contactbetween the element and the carrier is only within the collectedlubricant, and a non-circular ellipse, corresponding to the non-circularhalf ellipse shape of the convex curvature, is defined by a mathematicalformula for an ellipse in which the ellipse's largest width correspondsto the element width and a local radius of curvature at the ellipse'slargest height is smaller than a smallest radius of a curvature of thebelt.